ON THE MODE OF ACTION OF PREVENTIVE SERA. 97 



majority of the vibrios and causes very energetic clumping. If we 

 note the clarification of tubes containing an emulsion of cholera 

 and a very small dose of specific serum we find that it takes con- 

 siderable time for completion. It is partial at first, owing to a 

 rapid deposition of clumps, but proceeds gradually by the falling of 

 isolated motionless vibrios that are not clumped, and therefore sink 

 to the bottom slowly. 



We have then two sera which, although essentially different, have 

 similar properties. We might look on the horse as having naturally 

 the preventive substance against the cholera vibrio and on this 

 supposition we might postulate that the injection of horse serum 

 would give guinea-pigs a certain immunity against this organism.* 

 But the clumping substance of normal horse serum differs very 

 distinctly from the similar clumping substance of the immunized 

 guinea-pig. The first causes an agglutination of the red blood cor- 

 puscles of the normal guinea-pig, but the second does not. We may 

 conclude, then, that the property of clumping bacteria does not 

 belong exclusively to the specific preventive substance, and we can- 

 not refer to " clumping substance" and " preventive substance" as 

 synonymous. All that we can say is that in animals whose serum 

 normally is neither clumping nor preventive, vaccination may give 

 rise to both properties. 



Second: If the objection which we have just outlined were the 

 only one, we might use the clumping effect of preventive sera as a 

 means of diagnosis if we took care to use only an immune serum 

 from animals in whose serum no such property is present before im- 

 munization (the guinea-pig). 



But the effect which we are considering is never entirely specific, 

 even in serum from such animals. Gruber himself mentions certain 

 examples which invalidate the law of specificity. We must con- 

 sider this point rather in detail. We find that serum from guinea- 

 pigs vaccinated against the cholera vibrio (Eastern Prussia) agglu- 

 tinates energetically the vibrios from Eastern Prussia, of Massaouah 

 and less completely, but very distinctly, the colon bacillus. And 



* This fact has been noted by Pfeiffer and we can confirm it. The preventive 

 power, however, is never very strong. We may add that the subcutaneous injec- 

 tion of 3 c.c. of horse serum in the guinea-pig markedly increases the bactericidal 

 property of the animal. The increase, however, is not nearly so great as that 

 caused by specific serum. 



